1. Field of the Invention
This invention relates to a liquid crystal display apparatus in which color display information is converted into information about luminance of liquid crystal display used for driving a liquid crystal so as to provide a liquid crystal display and a method of performing a liquid crystal display, and more particularly to this type of liquid crystal display apparatus and method capable of alleviating flicker in picture and display flow which occur when display data of a display form pursuant to the dither method is displayed in accordance with gradation display of luminance.
The dither method referred to herein signifies a technique of realizing binary display of graded images of various half tones by making use of human visual characteristics, as well known in the art.
2. Description of the Prior Art
A frame base thin-out method has been proposed to achieve gradation display. That is, a liquid crystal is driven in accordance with an effective value of voltage applied to one dot and luminance of display is proportional to the effective value. In the frame base thin-out method, within a predetermined number of frames, some frames are turned on while the remaining frames are turned off and the rate at which the frames are turned on and turned off is call a thin-out rate and the rate is repeated to control the effective value of the applied voltage to the liquid crystal display, thereby performing, for example, half tone display of luminance in proportion to the effective value. However, the frame base thin-out method has a disadvantage that a flicker occurs in the image display each time a "turn on" operation is switched to a "turn off" operation and vice versa. Also, when dots are thinned out at the same timing over the entire screen, a flicker in the image display occurs to degrade the display quality of the image. Therefore, to eliminate the problem of flicker, the dot base thin-out method has been proposed.
With reference to FIGS. 4 and 5A to 5E, the dot base thin-out method will be described in greater detail. FIG. 4 illustrates a fundamental dot set in the dot base and FIGS. 5A to 5E show thin-out operation effected at a period of four frames.
Referring to FIG. 4, in the dot base thin-out operation is carried out in unit of a fundamental dot set 18 of 4 dots consisting of 2 dots in X direction (one odd dot and one even dot) and 2 dots in Y direction (one odd dot and one even dot) on the screen of a liquid crystal panel 17.
Within a frame defined by the fundamental dot set 18, dots are thinned out at different timings for two groups of which one has two staggered dots represented by .alpha. and the other has two staggered dots represented by .beta.. This thin-out operation will be described specifically with reference to FIGS. 5A to 5E. In these Figures, turned-on dots are depicted by hatched dots.
FIG. 5B shows a display mode at a thin-out rate of 1/4 in which any one of the four dots constituting the fundamental dot set is turned on once over 4 frames. At a first timing for the dots .alpha., dots .alpha.1 (the dots .alpha. particularly indicated for a first frame) are turned on within the first frame and dots .alpha.2 to .alpha.4 are turned off within the remaining frames. At a second timing for the dots .beta., dots .beta.3 (the dots .beta. particularly indicated for a third frame) are turned on within the third frame and the dots .beta.1, .beta.2, .beta.4 are turned off within the remaining frames. FIGS. 5C and 5D illustrates similar thin-out modes.
More specifically, in FIG. 5C, at the first timing for the dots .alpha., the dots .alpha.1 within the first frame and the dots .alpha.2 within the second frame are turned on with the dots .alpha.3 and .alpha.4 within the remaining frames turned off, and at the second timing for the dots .beta., the dots .beta.3 within the third frame and the dots .beta.4 within the fourth frame are turned on with the dots .beta.1 and .beta.2 within the remaining frames turned off.
In FIG. 5D, at the first timing for the dots .alpha., the dots .alpha.1 within the first frame, the dots .alpha.2 within the second frame and the dots .alpha.4 within the fourth frame are turned on with the dots .alpha.3 within the remaining frame turned off and at the second timing for the dots .beta., the dots .beta.2 within the second frame, the dots .beta.3 within the third frame and the dots .beta.4 within the fourth frame are turned on with the dots .beta.1 within the remaining frame turned off. FIGS. 5A and 5E illustrate perfect turn-off display and perfect turn-on display, respectively.
A prior art employing the dot base thin-out method described as above does not take the aforementioned dither technique and conventionally, when the dither method and the dot base thin-out method are used in combination, there arises a problem that the display flow is increased and the picture quality degradation is aggravated.